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Old 7th February 2012, 02:42 PM   #1
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Default Toroidal transformer on tube amp

Why are toroids so well regarded in solid state amps, but barely seldom seen on tube amplifiers? They are said to send less EMI and interference to sorrounding components, and some other good features.
Is there any reasong to be "so good" on solid state designs, but not in tube amplifiers? What about using them as output transformers?

I have NEVER used EI transformers, always sticked on toroidals. But I have never made a tube amplifier, anyway.

Thank you guys,
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Old 7th February 2012, 03:18 PM   #2
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I think that one reason is that there are not so many suitable toroids available for tube amps.
An other reason is that tube amp constructors are conservative.
And third reason is that transformers are part of the outlook and desing of tube amplifier.
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Old 7th February 2012, 03:31 PM   #3
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Conservative, in what sense? In using a 200W rated trafo for a 50w amp? Or conservative in the sense "I love stuff from 50 years ago"?

Maybe it worths to order a custom made toroidal, will think about that.

Coming from the SS world, I see that almost all tube amplifiers follow the same aesthetic designs rules. It may happen as well in the SS world, but coming from there, I am unable to notice
Builders use to have trafos and tubes exposed out there, without any covering. I wouldn't even think about having those hot (both electrically and termally) devices exposed to anyone who may come by and touch them by accident. That includes me and similar pets. Why not just cover them with a cheap bird cage of the proper size and adapted? That should mantain visibility for aesthetic reasons, and allows heat to be radiated and dissipated.
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Old 7th February 2012, 03:55 PM   #4
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Commonly SS amps are not using signal trafos. So saying SS favors toroid cores we better reverb as PS trafos favor toroid ones.

Signal trafos (or "tubes") implementing sophisticatedly sectioned windings very hard to perform in case of toroid form-factor. And once all trafos including big and heavy OT are not toroid core’s ones it might make sense implement PS trafo with a similar no-toroid core design.

Double C (U) core seems to be the right approach. Plitron makes toroid audio
Audio Output Transformers | Plitron
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Old 7th February 2012, 04:11 PM   #5
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The toroids for power xfmrs usually send out less magnetic interference if they are made right. (the section near where the wires come out can be a problem if the windings don't cover 100% of the core there).

But the power toroids send a great deal more conducted electrical noise thru themseleves from the power line to the secondaries due to their high primary to secondary capacitance and low leakage inductance (unless internal shielding is incorporated, not common on toroids though). The E-I power types for tube gear have low capacitance primary to secondary, and almost always have a grounded shield layer in between. The higher leakage inductance helps isolation too.

For output xfmrs (OT), the toroid versions are more difficult to make due to the high turns count and the high distributed capacitance. Special (expensive) winding techniques are required. And HV isolation (low capacitance) between the primary ends while maintaining close magnetic coupling is difficult. One can get most of the magnetic advantages of the toroid (low leakage inductance)by using cut cores or long E cores which are easier to wind.
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Old 7th February 2012, 05:38 PM   #6
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Quote:
Originally Posted by regiregi22 View Post
Conservative, in what sense? In using a 200W rated trafo for a 50w amp? Or conservative in the sense "I love stuff from 50 years ago"?
Probably the latter.

Antek Inc provides decent toroids for tube amps - www.antekinc.com

~Tom
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Old 7th February 2012, 06:15 PM   #7
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I have posted several times regarding this subject. Despite certain difficulties, toroids are really worth trying.

This is my draft build of push-pull amp using all-toroid design.
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File Type: jpg au111_v1.1_draft_assembly_600px.jpg (305.0 KB, 660 views)
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Old 12th February 2012, 01:44 PM   #8
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Thanks for all your answers! They've helped me a lot in knowing the reasons behind choosing EI.
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Old 12th February 2012, 06:08 PM   #9
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Quote:
Originally Posted by regiregi22 View Post
? Or conservative in the sense "I love stuff from 50 years ago"?
Yep thats the answer. Try suggesting a switching power supply and watch what happens. Antek sells some nice toroids for tube amps and at pretty good prices too. They also sell http://www.antekinc.com/images/160.png
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Old 12th February 2012, 09:16 PM   #10
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Thanks for your input!
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